1. Field of the Invention
The present invention relates to a technology for removing dew gathered in an image forming apparatus due to condensation.
2. Description of the Related Art
An image forming apparatus includes heat generating constituent elements such as various motors and a fixing unit. The heat generated by those elements leads to rise in the internal temperature of the image forming apparatus. The temperature difference between the internal temperature and the outside temperature leads to dew condensation in the image forming apparatus. Particularly, when the fixing unit applies heat and pressure to a recording medium (hereinafter, “sheet”) for fixing an image thereon in a low-temperature high-humidity environment, the moisture in the sheet vaporizes and builds up dew condensation in a conveying path near the fixing unit. If a sheet picks up the dew while being conveyed, the wet sheet may get jammed or skewed. Moreover, black spots appear on the wet sheet when an image is transferred thereon and the image quality degrades.
Japanese Patent Application Laid-open No. H8-234649 discloses an image forming apparatus with a dew removal mode. When the dew removal mode is implemented, a photosensitive drum is rotated without forming thereon an electrostatic latent image. A sheet is then conveyed over the photosensitive drum to remove dew condensation from the surface of the photosensitive drum. The wet sheet is then discharged to a discharge unit without forming an image thereon.
Moreover, Japanese Patent Application Laid-open No. 2006-206236 discloses an image forming apparatus that includes a dew condensation sensor for sensing dew condensation in a conveying path of the sheets and a control unit for controlling the conveyance of the sheets based on the result of the dew condensation sensor. More particularly, if the dew condensation sensor detects dew condensation during a warm-up period after switching ON the image forming apparatus, the control unit instructs a feeding unit to convey at least one sheet stacked therein via the conveying path such that the conveyed sheet removes the dew. The wet sheet is then discharged to a discharge unit without forming an image thereon.
Furthermore, Japanese Patent Application Laid-open No. 2005-274835 discloses an image forming apparatus that includes a conveying mechanism in which a discharging path and a re-conveying path for duplex image formation bifurcate at a position downstream of a fixing unit. During single image formation, a conveying roller (inverter roller) in the re-conveying path is subjected to idle rotation such that an air layer is formed around the conveying roller. The air layer prevents the moisture coming out of the fixing unit from settling in the re-conveying path, which remains idle during single image formation. Such a mechanism prevents dew condensation in the re-conveying path.
Meanwhile, in recent years, a sheet in a feeding unit is conveyed vertically upward and opposite to the direction of gravitational force to a discharge unit. Such a configuration is less conducive to dew condensation than an image forming apparatus having horizontal conveying mechanism. Howbeit, it is not possible to completely prevent dew condensation. Therefore, it is necessary to continue research on optimizing air flow design, sheet guiding design, and manufacturing material for an image forming apparatus.
However, the conventional technology of conveying blank sheets in a conveying path to remove the dew and then discharging the wet blank sheets without forming an image thereon leads to wastage of sheets.